Inertial measurement devices, such as gyroscopes and accelerometers, provide high-precision sensing, however, historically, their cost, size, and power requirements have prevented their widespread use in industries such as consumer products, gaming devices, automobiles, and handheld positioning systems.
More recently, MEMS devices, such as gyroscopes and accelerometers, have been gaining increased attention from multiple industries since micro-machining technologies have made fabrication of miniature gyroscopes and accelerometers possible. Miniaturization also enables integration of MEMS devices with readout electronics on the same die, resulting in reduced size, cost, and power consumption as well as improved resolution by reducing noise. Consumer products such as digital cameras, 3D gaming equipment, and automotive sensors are employing MEMS devices because of their numerous advantages. The demand for low cost, more sophisticated, and user-friendly devices by consumers has caused a steep rise in the demand of MEMS sensors, as they offer adequate reliability and performance at very low prices.
State-of-the-art MEMS devices, such as those disclosed in U.S. Pat. Nos. 7,578,189; 7,892,876; 8,173,470; 8,372,677; 8,528,404; 7,543,496; and 8,166,816, are able to sense rotational, i.e., angle or angular velocity of rotation around an axis, or translational motion, i.e., linear acceleration along an axis, around and along an axis. Techniques for manufacturing such devices using a process known as High Aspect Ratio Poly and Single Silicon (HARPSS) are disclosed in, for example, U.S. Pat. No. 7,023,065 entitled “Capacitive Resonators and Methods of Fabrication” by Ayazi, et al., and other publications.
As known, an imperfect MEMS gyroscope generates an undesired quadrature signal that is out of phase to the desired “rate” signal that indicates rotation about an axis. Such a quadrature error signal introduces an error component into the rate signal, leading to less than optimal output results from the MEMS gyroscope. In some instances, the quadrature error signal characteristics can overwhelm the rate signal generated by the MEMS gyroscope.
In vibratory gyroscopes, the quadrature error results from misalignment of the nodes and antinodes in the gyroscope's resonance modes with respect to pickoff electrodes. Misalignment of nodes and antinodes may occur due to crystalline misalignment and/or slanted sidewalls of the gyroscope's resonant member. As known, compensatory mechanisms must be utilized to precisely align the nodes and antinodes of the gyroscope's resonance modes to provide better performance with lower quadrature error/ZRO values. Such alignment can be done on a Z-axis gyroscope using electrostatic forces, however there has not been a mechanism to achieve such alignment with Bulk Acoustic Wave (BAW) vibratory planar gyroscopes.
In the case of BAW vibratory planar gyroscopes, among the operational resonance modes, there are modes with in-plane-only and out-of-plane-only movements. Such modes are not degenerate, making alignment difficult.
Accordingly, a need exists for an apparatus and technique to align the nodes and antinodes of the resonance modes of a BAW vibratory planar gyroscope.